1. Field of the Invention
The present invention relates to a substrate processing apparatus which coats a thin plate-like substrate (hereinafter "substrate"), such as a semiconductor substrate and a glass substrate of liquid crystal, with a chemical such as a resist.
2. Description of the Prior Art
In general, a substrate such as described above is coated with a resist which is photosensitive to light and which is used to form a pattern. It is necessary to change the film thickness of the applied coating resist in accordance with a characteristic which the substrate is required to have.
In a conventional approach, during coating of a substrate with a resist, the resist is injected through a nozzle while rotating the substrate so that the substrate is coated uniformly with a resist film. In order to change the film thickness of the resist according to this approach, methods such as (1) changing the number of rotations of the substrate and (2) using a resist having a different viscosity are used. More particularly, when the number of rotations of the substrate is changed, the greater number of times the substrate is rotated, the thinner the resist film becomes, whereas the smaller number of times the substrate is rotated, the thicker the resist film becomes. Meanwhile, a resist having a different viscosity is used, the greater the viscosity of the resist, the thicker the resist film becomes, whereas the smaller the viscosity of the resist, the thinner the resist film becomes.
In, recent years substrates have become larger and larger in diameter, with some substrates as large as 300 mm or larger in diameter being manufactured. With respect to a substrate having such a large diameter, the number of rotations the substrate can be rotated in order to uniformly spread resist is limited, and therefore, to change the number of rotations the substrate is rotated in order to change the film thickness of the resist is difficult. Hence, in order to change the film thickness of the resist for the substrate which has such a large diameter, a method using a resist having a different viscosity is used.
FIG. 5 is a conceptual diagram of a conventional nozzle structure for the case where a resist having a different viscosity is used. As shown in FIG. 5, a plurality of nozzles are disposed for resists of different types. During coating with resist A, for example a low viscosity resist nozzle A-1 is used to form a thin resist film, a high viscosity resist nozzle A-2 is used to form a thick resist film, and a middle viscosity resist nozzle A-3 is used to form a medium thick resist film. In a similar manner, with respect to resist B and resist C as well, there are a plurality of nozzles disposed for necessary thicknesses. Thus, a number of nozzles are needed in a substrate processing apparatus as a whole, and hence, a number of pipelines are needed, which complicates the structure of the apparatus.